The specific aims of this proposal are designed to test the ideas of recurrent models of primary visual cortex V1, to understand the mechanisms of V1's role in vision. Aim 1 is about the importance of inhibition for orientation tuning in V1, based on the dynamics of responses compare to model predictions. Aim 2 examines the response of V1 neurons to contrast reversal as a function of orientation. Aim 3 is about the contrast dependence of Untuned Suppression and how it relates to the invariance or non- invariance of orientation tuning with contrast. Aim 4 is about spatial phase specificity and the specificity of local connections in the cortical network. The rationale is that a crucial differentiating feature between different models is how phase-specific are the interactions between neurons in the network. We will measure the spatial phase specificity of neurons in the local network, in different V1 layers, using a combination of single-unit, multi-unit, and local field potential recording. PUBLIC HEALTH RELEVANCE The relevance of this research to public health is in its advance in understanding how the visual area in the cerebral cortex works. Understanding the function of the visual cortex will aid in all aspects of treatment and diagnosis of visual disorders and mental disorders. The visual cortex is the region of the cerebral cortex that is closest to being understood, and our work is aimed at advancing this understanding.